Sanitary Engineer Licensure Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Design period

The assumed service life used to size a facility. Water treatment plants and transmission mains commonly use 10-20 years; distribution networks 20-30 years; pumps and mechanical equipment 5-10 years.

Peak hour factor

Ratio of maximum hourly demand to average daily demand, typically 2.5-3.0 for residential areas. Used to size distribution mains and service connections, not treatment plants.

Maximum day demand

Highest 24-hour demand in a year, usually 1.5-2.0 times average day demand. It sets treatment plant and transmission capacity, with fire flow added for main sizing.

Hazen-Williams formula

Empirical head loss equation for pressurized pipes: hf = 10.67 L Q^1.852 / (C^1.852 D^4.87) in SI units. The C coefficient ranges near 130-140 for new lined pipe.

Manning equation

Open-channel flow formula V = (1/n) R^(2/3) S^(1/2), used to size gravity sewers. Roughness n is about 0.013 for concrete and 0.011-0.012 for plastic pipe.

Self-cleansing velocity

Minimum flow velocity that keeps solids moving in a sewer, about 0.6 m/s at design flow and 0.75 m/s where heavy solids occur. Prevents deposition and sulfide generation.

Minimum sewer diameter

Smallest permitted public sewer size, usually 200 mm for mains and 150 mm for laterals. Larger diameters reduce blockage risk and allow inspection and cleaning equipment.

Manhole spacing

Manholes are required at every change in direction, slope, or diameter and at intervals of roughly 90-150 m on straight runs, to permit access for cleaning and inspection.

Drop manhole

A manhole with an internal vertical drop pipe, used where the incoming invert is more than about 0.6 m above the outgoing invert, to prevent splashing and erosion.

BOD5

Biochemical oxygen demand measured over five days at 20 degrees C, approximating biodegradable organic content. Domestic sewage is typically 200-220 mg/L; first-order decay applies with k near 0.17 per day.

Standard-strength wastewater

Typical untreated domestic sewage composition: BOD5 about 200-220 mg/L, suspended solids 200-240 mg/L, total nitrogen 35-45 mg/L, and total phosphorus 6-10 mg/L.

Grit chamber velocity

Chambers are designed to hold a horizontal velocity near 0.3 m/s so dense grit settles while lighter organic solids remain suspended and pass to downstream treatment.

Primary sedimentation overflow rate

Design surface overflow rate of 30-50 m3/m2·d at average flow, rising to 80-120 m3/m2·d at peak. Detention time is 1.5-2.5 h, removing 50-65% of suspended solids.

Food-to-microorganism ratio

F/M ratio expresses kg BOD5 applied per kg MLSS per day. Conventional activated sludge uses 0.2-0.4 per day; extended aeration uses 0.05-0.15 per day.

Solids retention time

Average time solids remain in the aeration system, controlling treatment performance. Conventional plants use 5-15 days; nitrifying or extended aeration plants need 20-30 days.

MLSS

Mixed liquor suspended solids, the biomass concentration in an aeration basin, normally maintained at 2,000-4,000 mg/L. It sets the solids loading on secondary clarifiers.

Secondary clarifier solids loading

Design parameter for activated sludge clarifiers, about 100-150 kg/m2·d at peak flow. Surface overflow rate is typically 16-32 m3/m2·d with 2-4 h detention.

Return activated sludge ratio

Flow of settled sludge returned to the aeration basin, expressed as a fraction of influent flow, usually 0.5-1.5. It maintains the desired MLSS concentration.

Oxygen demand per BOD removed

Aeration must supply roughly 1.0-1.4 kg of oxygen per kg of BOD5 removed, plus endogenous respiration demand, which increases with longer solids retention time.

Trickling filter organic loading

Low-rate filters receive 0.08-0.4 kg BOD per m3 of media per day; high-rate filters receive 0.4-1.0 kg BOD/m3·d with recirculation to improve distribution and nitrification.

Sludge thickening

Gravity thickening of waste sludge at 25-35 kg/m2·d raises solids from about 0.5-1.0% to 4-6%, reducing digester volume. Primary sludge starts at 4-6% solids.

Anaerobic digestion

Mesophilic digestion at 30-38 degrees C with 15-30 day retention and volatile solids loading of 0.5-1.5 kg VS/m3·d, destroying 40-60% of volatile solids and producing methane.

Chlorine CT concept

Disinfection effectiveness depends on residual concentration times contact time. Required CT rises as temperature falls and as pH rises, because hypochlorous acid dissociates.

UV disinfection dose

Ultraviolet light dose of about 30-40 mJ/cm2 is applied to secondary effluent for coliform reduction. Effectiveness depends on low turbidity and proper lamp cleaning.

Nitrification requirements

Ammonia oxidation needs solids retention time above about 10 days at 20 degrees C, dissolved oxygen above 2 mg/L, and alkalinity near 7.1 mg as CaCO3 per mg ammonia-N.

Rapid sand filter rate

Filtration rate of 4-12 m/h through 0.6-0.9 m of sand with effective size 0.45-0.55 mm. Backwash at 12-15 L/m2·s expands the bed about 20-25%.

Coagulation velocity gradient

Rapid mix uses a velocity gradient of 300-1,000 per second for 10-60 seconds; flocculation uses 10-75 per second for 15-30 minutes, tapering downward.

Alum coagulation pH

Alum doses of 10-50 mg/L perform best at pH 5.5-7.5, where aluminum hydroxide flocs form. Optimum pH shifts with raw water alkalinity and turbidity.

Service reservoir capacity

Storage sized at 25-35% of maximum day demand for equalizing flow, or roughly 15-20% of maximum day demand plus dedicated fire storage where fire flow is required.

Air gap backflow protection

A physical separation between supply outlet and the fixture's flood level, giving the highest protection against both backpressure and backsiphonage. Reduced pressure zone assemblies are next.

Trap seal depth

The water seal in a plumbing trap, normally 50-100 mm deep. It blocks sewer gas while allowing wastewater flow; improper venting causes seal loss by siphonage.

Septic tank retention

Household septic tanks provide 24-48 hours retention with 1,000-2,000 L capacity and store sludge and scum for 1-3 years. Effluent goes to a soil absorption field.